Magnetic biochar, preparation method and application thereof, and preparation method of organic fertilizer

Abstract

The invention belongs to the technical field of adsorption materials, and particularly relates to magnetic biochar, a preparation method and application thereof and a preparation method of an organic fertilizer. The invention provides a preparation method of magnetic biochar, which comprises the following steps: mixing farmland sludge and plant residues, and carbonizing to obtain sludge biochar; mixing the sludge biochar, an activating agent and water, and soaking to obtain an activated biochar system; ferric salt, an alkaline reagent and water are mixed, precipitation reaction and dehydration are sequentially carried out, and magnetic particles are obtained; mixing the magnetic particles, a surfactant and water, and modifying in an alkaline environment to obtain modified magnetic particles; mixing the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent; and mixing the activated biochar system with a magnetizing agent, and magnetizing to obtain the magnetic biochar. The magnetic biochar obtained by the method provided by the invention has a good adsorption effect on harmful substances such as bisphenol A, antibiotics, heavy metals and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorption materials, and specifically relates to magnetic biochar and a preparation method and application thereof, and a preparation method of organic fertilizer. Background Art

[0002] Composting agricultural waste is an economical, effective and environmentally friendly technical means that can effectively solve prominent contradictions such as the large amount of agricultural waste and the difficulty in using it. However, the compost often contains harmful substances such as endocrine disruptors (EDCs), antibiotics, heavy metals, pesticides, microplastics, etc., which will have adverse effects on plants and soil when the compost is re-applied to the soil. Bisphenol A (BPA) is a typical EDC. According to relevant biological and toxicological studies, BPA will have adverse effects on human health when it enters the environment. If there is a suitable method to remove it, it can improve the safety of compost applied to the soil and promote the high-quality development of agriculture. In response to this problem, at present, there are a lot of studies on pretreatment before composting, compost additives, and secondary fermentation. Biochar is one of the hot topics.

[0003] Biochar (BC) raw materials come from a wide range of sources, such as dead branches and leaves, straw, agricultural and forestry waste, livestock and poultry breeding waste, sludge, domestic garbage and other solid wastes. Its main components are lignin, cellulose, hemicellulose and mineral elements. BC has a certain adsorption effect on endocrine disruptors due to its rich carbon content, high specific surface area and relatively developed pore structure, but its adsorption effect is limited and it is difficult to separate endocrine disruptors. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing magnetic biochar. The magnetic biochar (MBC) obtained by the method provided by the present invention has good adsorption and separation effects on endocrine disruptors in compost.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing magnetic biochar, comprising the following steps: Mix farmland sludge and plant residues and carbonize them to obtain sludge biochar (SBC); The sludge biochar, the activator and water are mixed and soaked to obtain an activated biochar system; The iron salt, alkaline reagent and water are mixed, and precipitation reaction and dehydration are carried out in sequence to obtain magnetic particles; The magnetic particles, a surfactant and water are mixed and modified in an alkaline environment to obtain modified magnetic particles; mixing the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent; The activated biochar system and a magnetizing agent are mixed and magnetized to obtain the magnetic biochar.

[0006] Preferably, the farmland sludge is fruit and vegetable farmland sludge; the water content of the farmland sludge is 60-80%; the plant residues are fruit and vegetable plant residues; the mass ratio of the farmland sludge to the plant residues is 1-6:2-8; The carbonization temperature is 300-600° C. and the time is 2-8 hours.

[0007] Preferably, the activator is 5,5-dimethyl-1-pyrroline-N-oxide; the mass ratio of the sludge biochar to the activator is 10-50:1; The soaking time is 2 to 3 hours.

[0008] Preferably, the iron salt includes a divalent iron salt and a trivalent iron salt; the divalent iron salt includes one or more of ferrous sulfate, ferrous nitrate and ferrous chloride; the trivalent iron salt includes ferric chloride and / or polyferric chloride; the alkaline agent includes one or more of ammonia water, calcium hydroxide and sodium carbonate; The precipitation reaction time is 1-6 hours; the dehydration is heating dehydration; the heating dehydration temperature is 60-80° C. and the time is 20-40 minutes.

[0009] Preferably, the surfactant comprises an anionic surfactant and / or a cationic surfactant; the mass ratio of the magnetic particles to the surfactant is 150:0.1-0.8; The pH value of the alkaline environment is 7-8; the modification temperature is 90-100° C. and the modification time is 40-50 minutes.

[0010] Preferably, the complexing agent includes one or more of sodium isobutyl tripolyphosphate, ethylenediaminetetraacetic acid, citric acid and tartaric acid; and the mass ratio of the modified magnetic particles to the complexing agent is 100:0.5-1.

[0011] Preferably, the mass ratio of the sludge biochar in the activated biochar system to the modified magnetic particles in the magnetizing agent is 5 to 10:1; The magnetization temperature is 80-90° C. and the time is 2-3 hours.

[0012] The present invention also provides magnetic biochar obtained by the preparation method described in the above technical solution, wherein the particle size of the magnetic biochar is 74-150 μm and the specific surface area is 215.25-305.1 m 2 ·g - ¹.

[0013] The present invention also provides the use of the magnetic biochar described in the above technical solution in fertilizer preparation.

[0014] The present invention also provides a method for preparing an organic fertilizer, comprising the following steps: The compost raw material and the magnetic biochar are mixed and composted to obtain the organic fertilizer; the magnetic biochar is the magnetic biochar described in the above technical solution.

[0015] The present invention provides a method for preparing magnetic biochar, comprising the following steps: mixing farmland sludge and plant residues, carbonizing to obtain sludge biochar; mixing the sludge biochar, an activator and water, soaking to obtain an activated biochar system; mixing iron salt, an alkaline reagent and water, sequentially performing precipitation reaction and dehydration to obtain magnetic particles; mixing the magnetic particles, a surfactant and water, modifying in an alkaline environment to obtain modified magnetic particles; mixing the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent; mixing the activated biochar system and a magnetizing agent, magnetizing to obtain the magnetic biochar. The present invention adds plant residues as raw materials to farmland sludge, so that the oxygen-containing functional groups on the surface of the obtained biochar are more abundant, the pore structure is more developed, and the specific surface area is larger, which significantly improves the adsorption performance. The prepared magnetic biochar mainly adsorbs BPA in fertilizers and inorganic substances such as phosphate, nitrate nitrogen, and fluorine through pore filling, hydrogen bonding, hydrophobic action and electrostatic action. When the pH value is low, the Fe-O + H2 sites can also electrostatically adsorb NO3 - and F - In addition, the magnetic biochar has strong magnetism, which enables it to separate from the compost product with the help of external magnetic equipment after absorbing harmful substances such as BPA, thus avoiding adverse effects on the soil and the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 This is a schematic diagram of the process of applying the magnetic biochar obtained in Examples 1 to 3 to return organic fertilizer to the field; Figure 2 This is a test data chart of the adsorption capacity of bisphenol A of the magnetic biochar obtained in Example 2. DETAILED DESCRIPTION

[0018] The present invention provides a method for preparing magnetic biochar, comprising the following steps: Mix farmland sludge and plant residues and carbonize them to obtain sludge biochar; The sludge biochar, the activator and water are mixed and soaked to obtain an activated biochar system; The iron salt, alkaline reagent and water are mixed, and precipitation reaction and dehydration are carried out in sequence to obtain magnetic particles; The magnetic particles, a surfactant and water are mixed and modified in an alkaline environment to obtain modified magnetic particles; mixing the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent; The activated biochar system and a magnetizing agent are mixed and magnetized to obtain the magnetic biochar.

[0019] In the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art, and all raw materials are of analytical grade.

[0020] The invention mixes farmland sludge and plant residues, performs carbonization, and obtains sludge biochar.

[0021] In the present invention, the farmland sludge is fruit and vegetable plant farmland sludge; the fruit and vegetable plant farmland sludge is vine fruit and vegetable plant farmland sludge, and the water content of the farmland sludge can be 60~80%, and can also be 65~75%; the plant residues are fruit and vegetable plant residues, and in a specific embodiment, they can be watermelon vines, tomato vines, eggplant seedlings or bean seedlings; the mass ratio of the farmland sludge to the plant residues is 1~6:1~8, and in a specific embodiment, it can be 1:1 or 2:1.

[0022] In the present invention, the carbonization step further comprises drying, grinding and sieving the mixture of farmland sludge and plant residues in sequence; the drying step comprises natural drying and oven drying in sequence; the natural drying time is 32 to 48 hours, and in a specific embodiment, it can be 40 hours; the oven drying temperature is 60 to 80°C, and in a specific embodiment, it can be 60°C, 65°C, 70°C, 75°C or 80°C; the oven drying time is 12 to 20 hours, and in a specific embodiment, it can be 12 hours, 15 hours, 16 hours, 18 hours or 20 hours; the present invention does not have any restrictions on the grinding process. The present invention does not have any special limitation and can be carried out in a manner well known to those skilled in the art; the mesh size of the sieving screen is 100-120 meshes; the carbonization temperature is 300-600°C, and in a specific embodiment, it can be 400°C or 500°C; the time is 2-8h, and in a specific embodiment, it can be 4h or 6h; after the carbonization, the carbonization product is further ground and sifted in sequence; the present invention does not have any special limitation on the grinding process and can be carried out in a manner well known to those skilled in the art; the mesh size of the sieving screen is 100-120 meshes.

[0023] In the present invention, farmland sludge and plant residues are rich in organic matter, cellulose, lignin and various nutrients, which can be converted into biochar with high specific surface area and rich pore structure during pyrolysis. Farmland sludge and plant residues are widely available and low in cost. Using them to prepare biochar can realize the resource utilization of waste and reduce environmental pollution.

[0024] After obtaining the sludge biochar, the present invention mixes the sludge biochar, an activator and water, and soaks them to obtain an activated biochar system.

[0025] In the present invention, the mixing may include the following steps: dissolving the activator in water to obtain an activator solution; The sludge biochar and activator solution are first mixed.

[0026] In the present invention, the activator is 5,5-dimethyl-1-pyrroline-N-oxide; the mass ratio of the sludge biochar to the activator is 10-50:1, and in a specific embodiment, it can be 20-30:1; the mass ratio of the sludge biochar to water is 1-1.5:10, and in a specific embodiment, it can be 1:7. The present invention has no special limitation on the molar concentration of the activator solution, as long as the dosage ratio of the sludge biochar, the activator and the water is met.

[0027] In the present invention, the soaking time is 2 to 3 hours. In the present invention, the sludge biochar has more surface active sites under the action of the activator, and these active sites can undergo redox reactions with BPA, further improving its catalytic performance and promoting the degradation process of BPA.

[0028] In the present invention, the immersion further includes adjusting the pH value of the system to 6-8, and in specific embodiments, it can be 6, 6.5, 7, 7.2, 7.5 or 8. The present invention has no special requirements for the method of adjusting the pH value of the system, as long as the desired pH value can be achieved.

[0029] The invention mixes iron salt, alkaline reagent and water, and sequentially performs precipitation reaction and dehydration to obtain magnetic particles.

[0030] In the present invention, the iron salt includes a divalent iron salt and a ferric iron salt; the divalent iron salt includes one or more of ferrous sulfate, ferrous nitrate and ferrous chloride, and in a specific embodiment, it can be ferrous sulfate heptahydrate; the ferric iron salt includes ferric chloride and / or polyferric chloride, and in a specific embodiment, it can be ferric chloride hexahydrate; the mass ratio of the iron salt to water is 6~10.8g:10mL, and in a specific embodiment, it can be 7~9g:10mL, and can also be 8g:10mL; the mass ratio of the divalent iron salt to the ferric iron salt is 2~4:3~5, and in a specific embodiment, it can be 3:4; the alkaline reagent includes one or more of ammonia water, calcium hydroxide and sodium carbonate; the mass percentage of ammonia in the ammonia water is 50~60%, and in a specific embodiment, it can be 56%; the volume ratio of the alkaline reagent to water is 1:1~3, and in a specific embodiment, it can be 1:2. In the present invention, the iron salt mainly participates in catalyzing the oxidation reaction of BPA and promoting its degradation. The divalent iron salts are mainly involved in reduction reactions and precipitation reactions, while the trivalent iron salts are involved in oxidation reactions and hydrolysis reactions; under the joint action of the divalent iron salts and the trivalent iron salts, magnetic ferrosoferric oxide is generated.

[0031] In the present invention, the precipitation reaction time is 1-6 hours, and in a specific embodiment, it can be 2 hours; after the precipitation reaction, solid-liquid separation is also included; the dehydration is heating dehydration; the temperature of the heating dehydration is 60-80°C, and in a specific embodiment, it can be 70°C; the time is 20-40 minutes, and in a specific embodiment, it can be 30 minutes; after the dehydration, collection and washing are also included; the collection is magnet collection. In the present invention, the function of the washing is to wash away the remaining iron salt.

[0032] After obtaining the magnetic particles, the present invention mixes the magnetic particles, a surfactant and water, and performs modification in an alkaline environment to obtain modified magnetic particles.

[0033] In the present invention, the surfactant includes an anionic surfactant and / or a cationic surfactant; the anionic surfactant includes sodium dodecyl sulfate and / or sodium dodecylbenzene sulfonate; the cationic surfactant includes hexadecyltrimethylammonium bromide; in a specific embodiment, the surfactant can be sodium dodecyl sulfate; the mass ratio of the magnetic particles to the surfactant is 150:0.1-0.8, and in a specific embodiment, it can be 150:0.1, 150:0.2, 150:0.3, 150:0.4, 150:0.5, 150:0.6, 150:0.7 or 150:0.8. In the present invention, the surfactant plays the role of a surfactant in the degradation process of BPA, promoting the dispersion and dissolution of biochar. The mass ratio of the magnetic particles to water is 14-16:1, and in a specific embodiment, it can be 15:1.

[0034] In the present invention, the pH value of the alkaline environment is 7-8; the reagent providing the alkaline environment is sodium hydroxide solution; the temperature of the modification is 90-100°C and the time is 40-50 minutes; the modification also includes adjusting the pH and collecting; the pH value of the adjusted pH is 6.5-7.5, and in a specific embodiment, it can be 7; the collection is magnet collection. In the present invention, during the modification process, the surfactant is fully adsorbed on the surface of the magnetic particles.

[0035] After obtaining the modified magnetic particles, the present invention mixes the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent.

[0036] In the present invention, the complexing agent includes one or more of sodium isobutyl tripolyphosphate, ethylenediaminetetraacetic acid, citric acid and tartaric acid, and in a specific embodiment, it can be sodium isobutyl tripolyphosphate; the mass ratio of the modified magnetic particles to the complexing agent can be 100:0.5-1, and in a specific embodiment, it can be 100:0.5, 100:0.75 or 100:1. In the present invention, the role of the complexing agent is to participate in the degradation reaction of BPA. The mass ratio of the modified magnetic particles to water is 9-11:1, and in a specific embodiment, it can be 10:1.

[0037] In the present invention, the modified magnetic particles are washed before mixing; the washing is water washing; the number of washings is 3 to 5 times; the mixing includes stirring and ultrasound in sequence; the ultrasound time is 10 to 20 minutes, and in a specific embodiment, it can be 15 minutes.

[0038] After obtaining the activated biochar system and the magnetizing agent, the present invention mixes the activated biochar system and the magnetizing agent and magnetizes them to obtain the magnetic biochar.

[0039] In the present invention, the mass ratio of the sludge biochar in the activated biochar system to the modified magnetic particles in the magnetizing agent is 5-10:1. In specific embodiments, it can be 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1.

[0040] In the present invention, the temperature of the magnetization is 80-90°C, the time is 2-3h; the magnetization is carried out under stirring conditions; and the magnetization also includes solid-liquid separation, washing and drying. In the present invention, the washing is used to rinse the remaining activator and magnetizer on the magnetic biochar. The drying is drying; the drying temperature is 90-105°C.

[0041] The present invention adds plant residues as raw materials to farmland sludge, so that the oxygen-containing functional groups on the surface of the obtained biochar are more abundant, the pore structure is more developed, and the specific surface area is larger, which significantly improves the adsorption performance. The obtained magnetic biochar mainly adsorbs BPA in fertilizers and inorganic substances such as phosphate, nitrate nitrogen, and fluorine through pore filling, hydrogen bonding, hydrophobicity, and electrostatic effects. When the pH value is low, the Fe-O + H2 sites can also electrostatically adsorb NO3 - and F - In addition, the magnetic biochar has strong magnetism, which enables it to separate from the compost product with the help of external magnetic equipment after absorbing harmful substances such as BPA, thus avoiding adverse effects on the soil and the environment.

[0042] The present invention also provides magnetic biochar obtained by the preparation method described in the above technical solution, wherein the average particle size of the magnetic biochar is 74-150 μm, and can be 96-130 μm; the specific surface area of ​​the magnetic biochar is 215.25-305.1 m 2 ·g - ¹, can be 260~280m 2 ·g - ¹.

[0043] The magnetic biochar provided by the present invention has a strong adsorption capacity for bisphenol A due to its rich functional groups and pore structure on the surface, but is not limited to the adsorption of bisphenol A, and can also adsorb common organic and inorganic pollutants such as phenol, heavy metal ions, nitrogen oxides and phosphates.

[0044] The present invention also provides the use of the magnetic biochar described in the above technical solution in fertilizer preparation. As a specific embodiment of the present invention, the magnetic biochar can be used as an adsorbent material to adsorb endocrine disruptors and degrade them during the fertilizer preparation process, thereby improving the safety of composting; the fertilizer can be an organic fertilizer, and the organic fertilizer can be an organic compost.

[0045] The present invention also provides a method for preparing an organic fertilizer, comprising the following steps: The compost raw material and the magnetic biochar are mixed and composted to obtain the organic fertilizer; the magnetic biochar is the magnetic biochar described in the above technical solution.

[0046] In the present invention, the mass ratio of the magnetic biochar to the compost raw material is 3-9:100, and can also be 5-8.5:100.

[0047] In the present invention, the composting includes a heating period, a high temperature period and a cooling period in sequence; the temperature of the heating period is 20-50°C and the time is 2-4 days; the temperature of the high temperature period is 50-70°C and the time is 7-8 days; the temperature of the cooling period is 20-50°C and the time is 10-12 days; the composting process also includes photocatalysis. In the present invention, the complexation between BPA and magnetic biochar is affected by temperature, pressure and solvent. The higher the temperature, the higher the efficiency of magnetic biochar in degrading BPA. Photocatalysis can be used to promote the degradation of BPA by magnetic biochar. Through photocatalysis, the photosensitive active substances on the surface of magnetic biochar are used to generate active oxygen substances under light conditions, thereby degrading BPA. After the composting, oxidation treatment and / or photocatalytic degradation are also included. In the present invention, the role of oxidation treatment and photocatalytic degradation is to convert substances such as phenol, phenolic aldehyde, phenolic acid, etc. into harmless products.

[0048] The present invention applies magnetic biochar to organic fertilizers to achieve the effect of effectively adsorbing bisphenol A and other impurities, which is conducive to sieving out substances such as bisphenol A, antibiotics, and heavy metals from compost samples after adsorption, thereby improving the quality of fertilizers. It is also conducive to the reuse of waste. When magnetic biochar is added to compost, the porosity of the material after addition will increase, and the catalase activity, dehydrogenase activity, pH value and organic matter in the material will all increase. It can be seen that magnetic biochar can also regulate the composting process, reduce nitrogen loss, and increase the carbon content of the compost product, enriching the effect of biochar on the composting process.

[0049] Specifically, magnetic biochar has a rich pore structure, and BPA molecules can enter the pores through physical adsorption and interact with the pore walls. The hydroxyl groups on the surface of magnetic biochar can serve as active sites to promote the electron transfer process, and can hydrogen bond with the hydroxyl groups in BPA to form hydrogen bonded compounds. This hydrogen bonding can enhance the interaction between magnetic biochar and BPA, which is beneficial to the adsorption process. The surface of magnetic biochar is usually rich in hydrophobic groups, and BPA is a hydrophobic substance. The hydrophobic effect makes BPA molecules more inclined to adsorb on the surface of magnetic biochar, thereby achieving effective adsorption. The hydroxyl and carboxyl groups on the surface of magnetic biochar carry positive and negative charges, and electrostatic interactions occur with the corresponding groups in BPA during the adsorption process, which can help enhance the adsorption effect of BPA.

[0050] The hydroxyl and carboxyl groups on the surface of magnetic biochar can form hydrogen bonds or electrostatic effects with phosphate ions to adsorb phosphate. The pore structure of magnetic biochar is also conducive to the adsorption of phosphate. Phosphate is fixed on the surface of biochar through physical adsorption. The nitrogen-containing functional groups on the surface of magnetic biochar can form hydrogen bonds with nitrate nitrogen to achieve the adsorption of nitrate nitrogen. The fluorine-containing functional groups on the surface of magnetic carbon can form hydrogen bonds or electrostatic effects with fluoride to achieve the adsorption of fluorine. The pore structure and large surface area of ​​magnetic biochar are also conducive to the adsorption of fluoride ions, thereby improving the adsorption efficiency.

[0051] In order to further illustrate the present invention, the magnetic biochar provided by the present invention and its preparation method and application, and the preparation method of organic fertilizer are described in detail below in combination with the accompanying drawings and embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0052] Example 1 300 g of sludge (including 200 g of farmland sludge with a water content of 70% and 100 g of watermelon vines) was taken from the watermelon planting land in Shunyi Base, Beijing. The sludge was naturally air-dried for 48 h, and then dried in a drying oven at 60 °C for 12 h. The dried sludge was ground into fine powder, sieved through a 100-mesh sieve, and then the sieved sludge fine powder was placed in a box-type resistance furnace. The sludge fine powder was pyrolyzed and carbonized at 300 °C for 2 h. The carbonized sludge biochar crude product was cooled to room temperature and then ground and sieved through a 100-mesh sieve to obtain sludge biochar (SBC), which was stored in a sample bottle for later use.

[0053] Dissolve 3.6 g FeSO4·7H2O and 4.8 g FeCl3·6H2O in 10 mL water, then add 5 mL 56% ammonia solution and stir rapidly for 2 h to produce precipitation. Separate the generated precipitate from the water and heat to 80 °C for 20 min. Wrap nylon cloth on a magnet to collect the magnetic particles, and then rinse off the remaining salts with running water to obtain magnetic particles.

[0054] 150 g of the obtained magnetic particles were mixed with 10 mL of water, and 0.6 g of sodium dodecyl sulfate and 5 drops of sodium hydroxide solution were added thereto to make the pH value 7.5. The mixture was heated to 90°C for reaction for 50 min to allow the sodium dodecyl sulfate to be fully adsorbed on the surface of the magnetic particles. After the reaction was completed, hydrochloric acid was added and the pH value of the mixture dropped from 7.5 to 7.0. The modified magnetic particles were then collected using a magnet wrapped in nylon cloth, and the remaining liquid was discarded.

[0055] The collected modified magnetic particles were washed with water for 4 times, 100 g of the particles were put into a container, 0.75 g of sodium isobutyl tripolyphosphate and 9.25 g of distilled water were added, stirred and mixed, and ultrasonic treatment was performed for 10 minutes to obtain a magnetizing agent.

[0056] 50 g of sludge biochar was placed in 200 mL of 0.1 mol / L 5,5-dimethyl-1-pyrroline-N-oxide solution and soaked for 2 h, and the pH value was adjusted to 7.2 to obtain an activated biochar system; After adding 10 g of magnetic agent to the activated biochar system, the system was heated to 85°C and stirred for 2.5 h, and then the crude magnetic biochar was separated. The residual 5,5-dimethyl-1-pyrroline-N-oxide and magnetic agent on the crude magnetic biochar were rinsed clean with running water, and then the crude magnetic biochar was placed in a drying oven at 100°C for drying to obtain a finished magnetic biochar product.

[0057] In the present invention, the average particle size of the magnetic biochar finally obtained is 96 μm and the specific surface area is 265.25 m² / g. These parameters show that the specific surface area of ​​the biochar is significantly increased by the modification treatment, which helps to improve its adsorption performance.

[0058] Example 2 Magnetic biochar was prepared according to the technical scheme described in Example 1, except that the dosage of FeSO4·7H2O was 2.4 g and the dosage of FeCl3·6H2O was 3.6 g.

[0059] Example 3 Magnetic biochar was prepared according to the technical scheme described in Example 1, except that the dosage of FeSO4·7H2O was 4.8 g and the dosage of FeCl3·6H2O was 6 g.

[0060] Application Example 1 Figure 1The schematic diagram of the process of applying the magnetic biochar obtained in Examples 1 to 3 to the return of organic fertilizer to the field. The specific process includes: using compost material as the experimental test raw material, adding magnetic biochar (the mass ratio of compost material to magnetic biochar is 100:3~7), BPA molecules are first adsorbed on the surface of magnetic biochar by physical adsorption, BPA temporarily stays on the surface of magnetic biochar, and then chemically reacts with the active sites on the surface of magnetic biochar to form chemical bonds, chemical adsorption involves hydrogen bonds, π-π stacking and other interactions, on the basis of chemical adsorption, BPA molecules react with the functional groups on the surface of magnetic activated carbon, wherein a partial structure of BPA forms a chemical bond with the functional groups on the surface of activated carbon, and the magnetic biochar degrades BPA by chemical adsorption to produce organic substances such as phenol, phenolic compounds, and phenolic acid. First, analytical methods such as chromatography-mass spectrometry are used to identify and quantify the degradation products, determine the main types of degradation products and their concentrations, use oxidation treatment to convert organic oxides such as phenol into harmless products, and use photocatalytic degradation to degrade organic matter such as phenolic acid under light conditions and convert them into harmless substances. After the treatment is completed, an external magnetic field is used to separate the magnetic biochar from it, and analytical instruments are used to monitor the status of the treated materials to ensure that the degraded materials are effectively treated and meet the agricultural fertilizer standards, thereby ensuring the safe application of fertilizers.

[0061] The concentration of BPA before and after the degradation of magnetic biochar obtained in Examples 1 to 3 (the mass ratio of compost material to magnetic biochar was 100:8.5) was detected by gas chromatography-mass spectrometry. The experimental conditions were carried out in a 50 mL beaker, and the magnetic stirrer conditions were set to a constant temperature of 25 °C and a stirring speed of 700 r / min. In the constant temperature and constant speed equipment, the prepared sludge-based magnetic biochar was mixed with bisphenol A solution (10 mg / L) for a reaction time of 12 min. Samples were taken at regular intervals, and the pollutant concentration was detected using a high performance liquid chromatograph. The content of BPA in the material is shown in Table 1.

[0062] Table 1 Concentration data before and after the degradation of BPA by magnetic biochar obtained in Examples 1 to 3

[0063] As shown in Table 1, the dosage of FeSO4·7H2O and FeCl3·6H2O is 3.6g and 4.8g respectively, and the adsorption amount is 6.54mg / g; the dosage of FeSO4·7H2O and FeCl3·6H2O is 2.4g and 3.6g respectively, and the adsorption amount is 4.43mg / g; the dosage of FeSO4·7H2O and FeCl3·6H2O is 4.8g and 6g respectively, and the adsorption amount is 5.26mg / g. It can be seen that increasing the dosage of FeSO4·7H2O and FeCl3·6H2O can first increase the adsorption amount and then reduce the adsorption amount, and the adsorption amount of Example 1 is the highest. The changes in BPA concentration before and after adsorption are as follows: the BPA concentration before adsorption was 1.42 mg / L, and the BPA concentration after adsorption was 0.28 mg / L; the BPA concentration before adsorption was 1.53 mg / L, and the BPA concentration after adsorption was 0.73 mg / L; the BPA concentration before adsorption was 1.45 mg / L, and the BPA concentration after adsorption was 0.54 mg / L. From these data, we can see that the BPA concentration after adsorption has decreased, indicating that the magnetic particles have a certain adsorption effect on BPA. Example 1 has the best adsorption effect, which may be because the higher FeSO4·7H2O and FeCl3·6H2O dosages lead to the generation of more magnetic particles, thereby increasing the adsorption amount and adsorption rate.

[0064] Application Example 2 Using sequencing batch aerobic fermentation equipment, 20 kg of watermelon vines and sludge from the land where they were used were taken as compost raw materials (including 10 kg of farmland sludge with a water content of 70% and 10 kg of watermelon vines), and the magnetic biochar obtained in Example 2 was used in an amount of 0.6 kg, 1 kg, and 1.4 kg respectively. After mixing evenly, the mixture was placed in a fermentation bin. After 15 days of fermentation, the material was taken out and mixed thoroughly with the raw materials. The obtained compost product was subjected to bisphenol A (BPA) content determination and other index analysis. The test results are shown in Figure 2 and Table 2.

[0065] Table 2 Concentration data before and after degradation of BPA by different dosages of magnetic biochar obtained in Example 2

[0066] Depend on Figure 2 It can be seen that when the biochar application amount is 5% (the magnetic biochar dosage is 1 kg), the compost product quality is the highest and the biochar utilization rate is the highest.

[0067] As shown in Table 2, the magnetic biochar provided by the present invention has a good adsorption and separation effect on endocrine disruptors in compost. As the amount of magnetic biochar increases, the concentration of heavy metals in the compost generally decreases, indicating that the magnetic biochar has a good adsorption effect on heavy metals. In particular, when the amount of magnetic biochar is 1.4 kg, the adsorption effect on Cu, Pb, Zn, Cr and Cd is most significant. This provides strong data support for the application of magnetic biochar in compost.

[0068] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing magnetic biochar, characterized in that: The following steps are involved: Mix farmland sludge and plant residues and carbonize them to obtain sludge biochar; The sludge biochar, the activator and water are mixed and soaked to obtain an activated biochar system; The iron salt, alkaline reagent and water are mixed, and precipitation reaction and dehydration are carried out in sequence to obtain magnetic particles; The magnetic particles, a surfactant and water are mixed and modified in an alkaline environment to obtain modified magnetic particles; mixing the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent; The activated biochar system and a magnetizing agent are mixed and magnetized to obtain the magnetic biochar.

2. The preparation method according to claim 1, characterized in that: The farmland sludge is fruit and vegetable farmland sludge, and the water content of the farmland sludge is 60-80%; the plant residues are fruit and vegetable plant residues; the mass ratio of the farmland sludge to the plant residues is 1-6:2-8; The carbonization temperature is 300-600° C. and the time is 2-8 hours.

3. The preparation method according to claim 1, characterized in that: The activator is 5,5-dimethyl-1-pyrroline-N-oxide; the mass ratio of the sludge biochar to the activator is 10-50:1; The soaking time is 2 to 3 hours.

4. The preparation method according to claim 1, characterized in that: The iron salt includes a divalent iron salt and a trivalent iron salt; the divalent iron salt includes one or more of ferrous sulfate, ferrous nitrate and ferrous chloride; the trivalent iron salt includes ferric chloride and / or polyferric chloride; the alkaline agent includes one or more of ammonia water, calcium hydroxide and sodium carbonate; The precipitation reaction time is 1-6 hours; the dehydration method is heating dehydration; the heating dehydration temperature is 60-80° C. and the time is 20-40 minutes.

5. The preparation method according to claim 1, characterized in that: The surfactant includes an anionic surfactant and / or a cationic surfactant; the mass ratio of the magnetic particles to the surfactant is 150:0.1-0.8; The pH value of the alkaline environment is 7-8; the modification temperature is 90-100° C. and the modification time is 40-50 minutes.

6. The preparation method according to claim 1, characterized in that: The complexing agent includes one or more of sodium isobutyl tripolyphosphate, ethylenediaminetetraacetic acid, citric acid and tartaric acid; the mass ratio of the modified magnetic particles to the complexing agent is 100:0.5~1.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the sludge biochar in the activated biochar system to the modified magnetic particles in the magnetizer is 5-10:1; The magnetization temperature is 80-90° C. and the time is 2-3 hours.

8. The magnetic biochar obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The particle size of the magnetic biochar is 74-150 μm, and the specific surface area is 215.25-305.1 m 2 ·g - ¹.

9. Use of the magnetic biochar according to claim 8 in fertilizer preparation.

10. A method for preparing an organic fertilizer, characterized in that: The following steps are involved: The compost raw material and the magnetic biochar are mixed and composted to obtain the organic fertilizer; the magnetic biochar is the magnetic biochar according to claim 8.

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